[GitHub] [spark] HyukjinKwon commented on a change in pull request #27517: [WIP][SPARK-29721][SQL] Prune unnecessary nested fields from Generate without Project

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HyukjinKwon commented on a change in pull request #27517: [WIP][SPARK-29721][SQL] Prune unnecessary nested fields from Generate without Project
URL: https://github.com/apache/spark/pull/27517#discussion_r376891150
 
 

 ##########
 File path: sql/catalyst/src/main/scala/org/apache/spark/sql/catalyst/optimizer/NestedColumnAliasing.scala
 ##########
 @@ -155,6 +161,56 @@ object NestedColumnAliasing {
     case MapType(keyType, valueType, _) => totalFieldNum(keyType) + totalFieldNum(valueType)
     case _ => 1 // UDT and others
   }
+}
+
+/**
+ * This prunes unnessary nested columns from `Generate` and optional `Project` on top
+ * of it.
+ */
+object GeneratorNestedColumnAliasing {
+  def unapply(plan: LogicalPlan): Option[LogicalPlan] = plan match {
+    // Either `nestedPruningOnExpressions` or `nestedSchemaPruningEnabled` is enabled, we
+    // need to prune nested columns through Project and under Generate. The difference is
+    // when `nestedSchemaPruningEnabled` is on, nested columns will be pruned further at
+    // file format readers if it is supported.
+    case Project(projectList, g: Generate) if (SQLConf.get.nestedPruningOnExpressions ||
+        SQLConf.get.nestedSchemaPruningEnabled) && canPruneGenerator(g.generator) =>
+      // On top on `Generate`, a `Project` that might have nested column accessors.
+      // We try to get alias maps for both project list and generator's children expressions.
+      NestedColumnAliasing.getAliasSubMap(projectList ++ g.generator.children).map {
+        case (nestedFieldToAlias, attrToAliases) =>
+          val newChild = pruneGenerate(g, nestedFieldToAlias, attrToAliases)
+          Project(NestedColumnAliasing.getNewProjectList(projectList, nestedFieldToAlias), newChild)
+      }
+
+    case g: Generate if SQLConf.get.nestedSchemaPruningEnabled &&
+        canPruneGenerator(g.generator) =>
+      // For the child outputs required by the operator on top of `Generate`, we do not want
+      // to prune it.
+      val requiredAttrs = AttributeSet(g.requiredChildOutput)
 
 Review comment:
   nit: maybe -> `requiredChildAttrs`

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